Electrical inductive apparatus



June 18, 1968 I R. P. MILLER ETAI. 3,389,302

ELECTRICAL INDUCTIVE APPARATUS Filed Oct. 21, 1965 2 Sheets-Sheet 2 FIG, 4 CIRCUIT BREAKER 45 L5' 'mmwr C'RCU'T INvENToRs FIG. 5 BREMER ROBERT P. MILLER (L49 49 DONALD P. sHAw United States Patent O 3,389,302 ELECTRECAL INDUCTIVE APPARATUS Robert l. Miller, Webster Groves, and Donald P. Shaw,

Brentwood, Mo., assignors to Wagner Electric Corporation, St. Louis, Mo., a corporation of Delaware Filed st. 2.1, 1965, Ser. No. 499,232 19 Claims. (Cl. 317-15) ABSTRACT 0F THE DISCLOSURE A transformer operable on different supply voltages having switch means to selectively connect the primary in a first winding arrangement in which a rst section is connected in series with fuse means and parallel-connected sections, said first section having a different nurnber of turns than the other sections, and a second winding arrangement in which all of the sections are in series with each other and other fuse means, all turns of the primary being conductive in both of the arrangements, the fuse means effective on the first winding arrangement being maintained in the circuit in the second winding arrangement.

This invention relates to electrical inductive apparatus and more particularly to electrical inductive apparatus, such as transformers, having circuit protective means associated therewith.

Distribution transformers connected in an electrical distribution system are often provided with protective circuit interrupting means or fuses in the primary winding circuit within the transformer casing and, in many cases, with fuses or circuit breakers in the low voltage secondary winding or load circuit of the transformer. As is well known, distribution transformers having primary windings adapted for connection with two high voltage distribution supply lines, such as when the system is supplied power from a delta connected power source, two primary bushings are used and a fuse is connected at cach end of the primary winding so that both ends of the primary will be disconnected from the system upon the occurrence of a fault therein. The size or rating of the primary winding fuses must be coordinated with the secondary winding circuit breakers, if used, and the line fuses or protectivecircuit interrupting means at the substation or high voltage supply transformer that supplies the power to all of the distribution transformers connected to the supply lines of the distribution system. The primary winding fuses and secondary circuit breakers, if used, are correlated such that, upon an overload condition, the circuit breakers will disconnect the load quickly enough to prevent the primary fuses from disconnecting the primary winding from the supply line; and this avoids the necessity of replacing primary fuses vas a result of excessive loading. The primary fuses are also selected such that, upon the occurrence of afault or excessive current in the primary of the distribution transformer, the primary fuses will disconnect the primary winding from the supply line quickly enough to prevent the line fuses or circuit interrupting means at the substation transformer from disconnecting the entire distribution system from the substation transformer. In this way, a fault in one distribution transformer will result in only that transformer being taken off the line as opposed to having all of the distribution transformers taken olf the line.

Because the line losses increase and the system regulation becomes poorer as the load requirements on the distribution system increase, electric power companies often require distribution transformers equipped with means for changing the transformation ratio thereof, such as by Patented June 18, 1968 ice means of a tap changing switch, so that the supply voltage can be raised to reduce the line losses and improve the system regulation when desired. However, if the primary fuses are designed to provide optimum protection when the transformer is connected for operation at one supply voltage, the same primary fuses would not provide optimum protection when the transformer is connected for operation on the higher,k supply voltage. If the primary fuses are selected on the basis of a compromise, that is, selected so as to operate on both the lower and higher supply voltages in order to avoid the above-mentioned changing of fuses, then optimum circuit protection is not obtained when the transformer is connected for operation on the higher supply voltage or on the lower supply voltage. It is, therefore, desirable to utilize primary fuses that are selected to provide optimum circuit interrupting characteristics when the primary winding is adapted for operation on the lower supply voltage and other fuses selected to provide optimum circuit interrupting characteristics when the primary winding is connected for operation on the higher supply Voltage.

When the higher supply voltage value is a whole number multiple of the lower supply voltage value, the primary winding can be arranged in like winding sections that are changed or switched from parallel relationship to series relationship when the supply voltage is to be changed from the lower supply voltage value to the higher supply voltage value. In such an arrangement, s

the (higher current rated) fuses selected for operation on the lower supply voltage (higher current) may be connected to remain in the primary circuit for both the series and parallel winding connection to provide optimum circuit interrupting characteristics when the transformer is connected for operation on the lower supply voltage, these `fuses being essentially ineffective on the higher voltage (lower current) connection. Those fuses (lower current rated) that are selected to provide optimum circuit interrupting characteristics when the transformer is connected for operation on the higher supply voltage (lower current) are connected in series with the entire primary winding during transformer operation on the higher supply voltage but may be arranged to also be in the primary circuit when the transformer is connected for operation on the lower supply voltage; however, they must, of course, be connected in series with only a portion or section of the primary winding so that they do not carry the total primary current when the transformer is operating on the lower supply voltage.

When the ratio of the higher to the lower supply voltages is not an integer, that is, when one of the supply voltage values is not a whole number multiple of the other, the primary winding may be arranged in winding sections connected in parallel relation with each other when connected for operation on the lower supply voltage. When the transformer is to be operated on a higher supply voltage, the winding sections can be arranged such that only a portion of one winding section is connected in series with another winding section or sections in order to obtain the required turns ratio necessary for operating the transformer on the higher voltage. For the above lower supply voltage winding connection, the effective fuses (higher current rated) are connected in series with the parallel connected winding sections andthe lower current rated fuses may be each connected respectively in series with only one of the parallel connected Winding sections. For the above higher supply voltage connection, `the lower current rated fuses are connected in series with the effective portions of the primary winding and the higher current rated fuses, although they may be retained in the primary circuit, do not perform the basic circuit interrupting function. However, such a winding arrangement has the disadvantage of having an idle or inactive winding portion when the primary is connected for the hig-her supply voltage operation, that is, a portion of one winding section does not carry primary current. In such a case, upon the occurrence f a surge voltage, such as caused by lightning, the winding section having the idle portion acts like an autotransformer, and very high voltages may appear across the idle portion of the winding with the danger of an insulation breakdown or short. The greater the idle winding portion, the greater will be the danger of damage to the transformer.

It is, therefore, an object of the present invention to provide an improved electrical inductive apparatus wherein the above-mentioned disadvantages are substantially obviated.

Another object of the present invention is to provide electrical inductive apparatus having means for changing the connection of electrical windings thereof from one winding arrangement operable at a first voltage value to another'winding arrangement operable at a second voltage value wherein circuit protective means are utilized that can be selected to provide substantially optimum protective circuit interrupting characteristics when the electrical windings are operating on either of the first and second voltage values.

Another object is to provide a transformer having a novel winding circuit with protective circuit interrupting means associated therewith and with relatively simple switch means for switching the winding circuit from a circuit arrangement which is operable on a first voltage to a second circuit arrangement operable on a second voltage where the ratio of the first and second voltages is not a whole number, wherein the circuit interrupting means used can be selected to provide substantially-optimum circuit interrupting characteristics when the winding circuit is operating on the first voltage and when it is operating on the second voltage and wherein neither of the first and second winding arrangements require idle winding portions.

Another object is to provide a transformer of the abovementioned type which is disposed in a transformer tank and wherein the above-mentioned switching means is operable to effect the switching of the winding circuit from the first circuit arrangement to the second circuit arrangement as a result of the movement of a single switch actuator accessible from outside the transformer tank.

Still another object is to provide a transformer having novel circuit means for changing the transformation ratio thereof so that the transformer primary winding is selectively operable on either a first or a second supply voltage value where the supply voltage values are in a ratio that is no t a whole number, wherein protective circuit interrupting means are utilized which can be selected to provide optimum circuit interrupting characteristics when the transformer is operating on either of the supply voltage values, the entire primary winding is conductively connected in the primary circuit of the transformer when it is operating on either the supply voltage values, and with a minimum of winding connections.

These and other objects and advantages will become more apparent from the foregoing description and accompanying drawings.

In the drawings which illustrate preferred embodiments of the present invention,

FIG. 1 is an elevational View partly in section of a distribution transformer embodying the present invention but with certain conductive leads deleted for simplicitys sake,

FIG. 2 is an elevational view of the switch means of FIG. 1,

FIG. 3 is a sectional view of the switch means taken along the line 3--3 of FIG. 2,

FIG. 4 is a schematic diagram of the transformer of FIG. 1 with the windings thereof connected to provide a predetermined transformation ratio, and

FIG. 5 is a schematic diagram of the transformer of FIG. 1 with the windings thereof connected to provide a different transformation ratio.

Referring now to FIG. 1 of the drawings, a distribution transformer is shown which includes a transformer core and coil assembly 11 disposed within a transformer casing or tank 12. having a cover 13, the casing 12 being adapted to be substantially filled with a suitable dielectric, such as transformer oil (not shown). The c-ore and coil assembly 11 includes a three-legged magnetic core 14, a plurality of coils 15 surrounding the middle core leg, and a frame 17. The frame 17 includes upper and lower end plates 18 and 19, opposed side plates 20 and 21 interconnected, such as by lbolts 22, two upper spacer blocks 25 (one in view) at opposite sides of the core between the upper end of coils 15 and end plate 1S, and a pair of lower spacer blocks 26 (one in view) at opposite sides of the core between the coil 15 and lower end plate 19. The coils 15 and core 14 are firmly held in fixed relationship by the plates 18-21 and blocks 25 and 26.

A pair of spaced primary bushings 30 and 31 of insulating material, such as porcelain, extend through and are connected to the cover 13. A primary fuse 33 extends into the lower end of bushing 30 and has an upper terminal end threadedly and conductively connected to the lower end of a bushing conductor 34 having an upper terminal end 34a adapted for connection to a high voltage supply line 35. Similarly, a primary fuse 36 extends into the lower end of bushing 31 and has an upper terminal end threadedly and conductively connected to the lower end of a bushing conductor 37 which has an upper terminal end 37a connected to another high voltage supply line 38. Power lines 35 and 38 may be one phase of a three-phase power supply or substation high voltage transformer (not shown) which has a secondary connected in delta and a primary in Y. The fuses 33 and 36 have lower end terminals 39 and 40, respectively, and each provides a conductive terminal. Another pair of primary fuses 42 and 43 are shown secured to the top of the upper end plate 18 of frame 17. Fuse 42 has a pair of end terminals 44 and 45 and fuse 43 has a pair of end terminals 46 andy 47. Three secondary winding bushings 49 are shown connected to the wall of the casing 12 for connection to a load circuit, such as 12B/240 volt load circuit. A ratio changing switch 50, shown in detail in FIGS. 2 and 3, is mounted within casing 12 to the wall thereof and has an actuating shaft 51 extending through the casing wall and a manually rotatable member 51a fixed theretoexternally of the casing for operating the switch 5G.

As seen in FIGS. 4 and 5, the transformer coils 15 include a primary winding 52 and a secondary winding 53. The primary winding 52 incluudes three winding sections 55, 56 and 57, and the secondary winding 53 includes a pair of like winding sections 58 and 59 adapted for connecton with the secondary winding bushings 49. A conventional secondary winding circuit breaker, which may also be mounted in the transformer casing 12, is shown in block form connected in the secondary winding circuit to disconnect the secondary winding 53 from the load upon the occurrence of an overload condition. The switch S0, which is described in detail hereinafter, is connected in the primary winding circuit and is operable to change the transformation ratio of the transformer 10 when it is desired to change the voltage of the power supply or substation transformer and therefore the voltage between power supply lines 35 and 38.

Referring now FIGS. 2 and 3, the switch 50 includes an insulating panel 62 having a plurality of like stationary contacts 63 circumferentially arranged thereon, a movable contact member 64 connected to shaft 51 which is rotatable to selectively interconnect certain ones of the contacts 63, a second plurality of like stationary contacts 66 predeterminately circumferentially arranged on panel 62, and a second movable contact member 67 connected to shaft 51 which is rotatable to selectively interconnect certain ones of the contacts 66. Contacts 63 and 66 are fixed to the panel 62, such as by screws, with the contacts 63 and associated contact member 64 in planes spaced farther from panel 62 than the planes of contacts 66 and associated contact member 67. The contacts 63 are sequentially identified as contact 63a and. 63d, and the contacts 66 are sequentially identified as contacts 66a through 66C.

Movable contact member 64 includes an insulating member 68 keyed to shaft 51 and arcuate metal contacts 69 and 70 connected, such as by screws, to the opposite ends of member 68. Each of the contacts 69 and 70, when in an operable position, electrically interconnects two sucessive stationary contacts 63.

The movable contact member 67 includes an insulating member 72 keyed to the shaft 51 and an arcuate metal contact 73 connected to the insulating member, such as by screws. The contact 73, when in an operable position, electrically interconnects two successive stationary contacts 66.

The panel 62 is fixed, such as by screws, to a collar member 75 (FIG. 3) that extends through an opening 76 in the wall of casing 12 and which receives a nut 77 on the external end thereof for securing the switch 50 to the casing 12. The manually rotatable member 51a is keyed to the external end of shaft 51 and secured thereto by a nut 78.

Referring now to FIGS. 4 and 5, supply line 35 is connected to bushing terminal 34a which, in turn, is connected to fuse 33 within the bushing 30. The terminal 39 of fuse 33 is connected to terminal 44 of fuse 42 and to contact 66C of switch 50 by a lead 80. The other terminal of fuse 42 is connected to switch contact 66a by a lead 81. The left end of primary winding section 55 is connected by a lead 82 to switch contact 66b and the right end of section 55 is connected to the left end of primary winding section 56 and to switch contact 63d by a lead 83. The right end of section 56 is connected to switch contact 63b by a lead 84. The left end of primary winding section 57 is connected by a lead 85 to switch contact 63e and the right end thereof to terminal 46 of fuse 43. The other terminal 47 of fuse 43 is connected to switch contact 63a by a lead 86 and also to the terminal 40 of fuse 36 by a lead 87. The fuse 36 is connected at the opposite end thereof to bushing terminal 37a to which supply lead 38 is connected.

With the switch Si) in the position shown in FIG. 4, contacts 66b and 66C are conductively interconnected by movable contact '73 to connect fuse 33 between bushing terminal 34a and the left end of winding section 55. The right end of section 55 is connected to the left end of winding section 5,6 and also to the leit end of winding section 57 since contacts 63C and 63d are interconnected by mov able contact 70. The right end of section 56 is connected to terminal 40 of fuse 36 sincecontacts 63a and 63b are 'interconnected by movable contact 69. Thus, it is apparent ksupply voltage is 4800 volts switch is in the position shown in FIG. 4 and the voltage across each of the secondary winding sections 58 and 59 is 120 volts.

With the switch 50` in the position shown in FIG. 5, contacts 66a and 66b are interconnected by movable contact 73 to connect fuse 42 between bushing terminal 34a and the left end of winding section 55. The right end of section is connected to the left end of section 56, and the right end of section 56 is connected to the left end of section 57 since contacts 63b and 63e are interconnected by movable contact 70. When switch 59 is in the position shown in FIG. 5, the winding sections 55, S6 and 57 and fuses 42 and 43 are connected in series circuit relationship between the supply lines 35 and 38 to provide a different predetermined transformation or turns ratio with the secondary winding 53 shown in FIG. 4. The fuses 42 and 43 can be selected to provide optimum circuit interrupting characteristics when the transformer is operating on the higher of the two operating voltages (7620 volts), the switch being in the position indicated in FIG. 5. Fuses 33 and 36 are selected to have a higher current rating than fuses 42 and 43 since fuses 33 and 36 are effective on the relatively lower supply voltage (higher primary current) while the fuses 42 and 43 are etective on the relatively higher supply Ivoltage (lower primary current). Since the fuses 33 and 36 will normally have a higher current rating than that of fuses 42 and 43, they may be conveniently permanently connected to the bushing terminals 34 and 37, as shown, and in both positions of switch 50, that is, when the transformer is operating on either of the two supply voltage values. Of course, when the switch is in the position shown in FIG. 5, the fuses 33 and 36 carry the primary current but do not provide effective circuit interrupting operations. Also, while the fuses 33 and 36 are the effective fuses when the switch is in the position shown in FIG. 4, fuse 43 may be permanently connected in series with winding section 57, as shown in FIG. 4, as it will carry only the current of winding section 57 since it is connected in parallel with winding section 56.

In general, when the ratio of the relatively high supply line voltage, E1, to the relatively low supply voltage, E2, is not an integer, the primary winding sections are determined by the following simultaneous equations:

where rV1 is the voltage of the common series winding section, such as section 55, V2 is the voltage of each of the winding sections that are adapted for parallel connection when the supply voltage is E2, and N is the number of winding sections adapted to be connected in parallel with each other and which is equal to the integer next above the ratio of E1 to E2.

`In the example transformer, the higher supply line voltage E1 is 7620 and the lower supply line voltage E2 is 4800 so that the ratio of E1 to E2 is approximately 1.58; therefore, N=2 and there will be two winding Asections conected in parallel and one in series with the two parallel connected sections. Thus, substituing the known values in Equations 1 and 2 results in:

(1) Vlnr/2:7620 (2) n+1/2:4800

From these equations V1=1980 and V2=2820- Thus, primary winding section 55 is designed to have 1980 volts thereacross and each of the winding sections 56 and 57 is designed to have 2820 volts thereacross, the number of turns of these primary winding sections, of course, being in proportion to the designed voltage thereacross.

By arranging the primary winding into sections which include a plurality of like sections, such as sections S6 and 57, connectable in parallel relation, and a series or common section, such as section 55, and in accordance with the above simultaneous Equations l and 2, the

necessity of having an undesirable idle winding portion is avoided even though the ratio of the supply line voltages is not an integer.

When the supply line voltage is at the lower value and the switch 50 is in the position shown in FIG. 4, the fuses 33 and 36 are effective to disconnect the primary winding 52 from the supply lines 35 and 38 upon the occurrence of a transformer fault, such as a short in the primary winding. Fuses 33 and 36 are selected so that they will interrupt current therethrough before the line fuses or circuit interrupting means at the substation can operate to interrupt power to the supply lines 35 and 38 and the other distribution transformers connected thereto. Similarly, when the switch 50 is in the position shown in FIG. and the line voltage is at the relatively higher voltage, the fuses 42 and 43 will be effective to interrupt primary current before the substation circuit interrupting means can operate to interrupt power to the supply lines and 38. The effective fuses, being ahead of the primary winding or located at the ends of the primary winding, provide adequate protection for the line or substation circuit interrupting means.

With the hereinbefore described arrangement there are relatively few circuit lead connections and switch contacts required. Also, the ratio of transformer 10 can be easily and simply changed by rotating member 52 from outside the transformer casing 12 to change the switch from the position shown in FIG. 4 to that shown in FIG. 5 when it is desired to increase the line voltage.

If desired, the fuse 43 may also be disconnected from winding 57 when the transformer is to be operated on the lower supply voltage by suitably switching it out of the primary circuit, such as by use of additional contacts (not shown) on switch 50. `Furthermore, if desired, the fuses 33 and 36 may be switched out of the primary circuit when the transformer is to be operated on the higher supply voltage by relocating them and providing suitable contacts on switch 50.

From the foregoing, it is obvious that novel transformer means meeting the objects and advantages set forth hereinbefore, and others, are provided. It is to be understood that the foregoing description and the occompanying drawings have been given only by way of illustration and example, and that changes and alterations in the present disclosure, which will be readily apparent to one skilled in the art, are contemplated as within the scope of the present invention which is limited only by the claims which follow.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A transformer comprising a pair of transformer terminals, primary and secondary windings, said primary windings including first, second and third winding sections, first and second pairs of fuses, and switch means having first and second operating positions and connected to said winding sections and said fuses for changing the transformation ratio of said transformer, said switch means when in said first position interconnecting said first and second winding sections in parallel with each other and in series with said third winding section and said first pair of fuses between said transformer terminals to effect a first predetermined transformation ratio between said primary and secondary windings, said switch means when in said second position interconnecting said first, second and third sections and said second pair of fuses in series with each other between said transformer terminals to effect a second predetermined transformation ratio between said primary and secondary windings, one of said fuses of said first pair being connected between one of said transformer terminals and one end of said primary winding and the other of said fuses of said first pair being connected between the other of said transformer terminals and the opposite end of said primary winding when said switch is in said first position, one of said fuses of; said second pair being connected betwccn said one transformer terminal and said one end of said primary winding and the other of said fuses of said second pair being connected between said other transformer terminal and said `opposite end of said primary Winding when said switch is in said second position.

2. A transformer comprising a casing, a pair of primary bushing-s mounted to said casing each having a bushing conductor, said bushing conductors having first ends exterior of said casing for respective connection to a pair of power supply lines, a first pair of fuses having first ends thereof connected respectively to the ends of said bushing conductors opposite said first ends thereof, a core and coil assembly in said casing including a magnetic core, and primary and secondary widnings on said core, said primary winding including first and second equal winding sections and a third winding section, a Second pair of fuses mounted to said core and coil assembly, and switch means mounted within said casing and including switch actuating means extending through said casing with a portion thereof exterior of said casing for actuating said switch means from a first position to a second position in response to predetermined movement of said exterior portion, means connecting said winding sections and said fuses to said switch means, said switch means when in said first position interconnecting said first and second winding sections in parallel with each other and in series with said third section between the ends of said first pair of fuses opposite said first ends thereof, said switch means when in said second position interconnecting all of said winding sections and said secind pair of fuses in series with each other between said opposite ends of said first pair of fuses.

3. A transformer comprising a casing, a pair of transformer terminals adapted to be supplied power from a source of supply voltage that is subject to being changed from a first voltage value to a second voltage value which is of higher value than said first voltage value and wherein said second voltage value divided by said first voltage value yields a quotient that is not an integer, primary and secondary windings in said casing, said primary windiing including first and second winding sections each having a like predetermined number of turns and a third winding section having a different predetermined num- !ber of turns than said first and second winding sections, first and second fuse means in said casing, and switch means having first and second operating positions and connected to said sections and said fuse means, said switch means being mounted within said casing and including switch actuating means extending through a wall of said casing with a portion thereof exterior to said casing whereby said switch means is movable between said operating positions in response to movement of said exterior portion, said switch means when in said first position interconnecting said first and second sections in parallel with each other and in series with said third section and said first fuse means between said transformer terminals to effect a predetermined transformation ratio between said primary and secondary windings so that said transformer is operable when said supply voltage is at said first voltage value, said switch means when in said second position interconnecting said first, second and third sections and said second fuse means in series with each other between said transformer terminals to effect another predetermined transformation ratio between said primary and secondary windings so that said transformer is operable when said supply voltage is at said second voltage value, al1 of said turns of said winding sections being conductive when said transformer is in operation and said supply voltage is at said first voltage value and also when said supply voltage is at said second voltage value.

4. A transformer comprising a casing, a pair of primary bushing-s mounted to said casing eachY having a bushing conductor, said conductors having first ends cxterior of said casing for respective connection to a pair of power supply lines connected to a source of supply voltage that is subject to being changed from a first voltage value to a second voltage value which is of higher value than said first voltage value, a first pair of fuses having first ends thereof connected respectively to the ends of said bushing conductors opposite said first ends there-of, Ia core and coil assembly in said casing including a magnetic core, and primary and secondary windings on sa-id core, said primary winding including first and second equal winding sections-and a third winding section, a second pair of fuses mounted to said core and coil assembly, and switch means mounted within said casing and including switchk actuating means extending through said casing with a portion thereof exterior of said casing for .actuating said switch means from a first position to a second position in response to predetermined movement of said exterior portion, means connecting said winding sections and said fuses to said switch means, said switch means when in said first position interconnecting said first and second winding sections in parallel with each other and in series with said third section -between the ends of said first pair of fuses opposite said first ends thereof to provide a predetermined transformation ratio between said primary and secondary windings so that said transformer is opera'ble when said supply voltage is at said first voltage value, said switch means when in said second position interconnecting all of said winding sections and lsaid second pair of fuses in series with each other between said opposite ends of said first pair of fuses to provide a predetermined transformation ratio between said primary and secondary windings so that said transformer is operable when said supply voltage is at said second voltage value.

5. A tranformer comprising a casing; a pair of primary bushings mounted to said casing and having bushing conductors for respective connection to a pair of power supply lines; a coil and core assembly mounted within said casing and including a magnetic core and primary and secondary windings on said magnetic core; said primary winding including first and second equal winding sections and a third windingsecti-on; a switch mounted within said casing including first, second, third, fourth, fifth, sixth and seventh stationary conta-cts, movable contact means engageable with said stationary contacts and having first and second operable positions, said movable contact Imeans including first, second and third contact members, and actuating means connected with said movable contact means and extending through said casing with a portion thereof exterior of said casing for moving said .movable contact means from one of said o-perable positions to the other of said positions in response to predetermined movement of said exterior portion; first and second pairs of fuses; means connecting one end of one of said fuses of said first pair to one of said bushing .conductors and the other end thereof to a first circuit point; means connecting one end of the other fuse of said first pair to the other of said bushing conductors andthe other end thereof to a second circuit point; means connecting one end of one of said fuses of said second pair to said first circuit point and the other end thereof to said first contact; means connecting one end of the other fuse of said second pair to Isaid second circuit point and the other end thereof to one end of said first section; means connecting said first circuit point to said second contact; means connecting one end of said third section to said third conta-ct; means connecting the other end of said third section and one end of said second section to a third circuit point; means connecting said third circuit point to said fourth contact; means connecting the other end of said second section to said fifth contact; means connecting the other end of said first section to said sixth contact; and means connecting said second circuit point to said seventh contact; said first'contact member being in engagement with and interconnecting said second and third contacts, said second contact member being in engagement with and interconnecting said fifth and seventh contacts,

and said third contact member being in engagement with and interconnecting said fourth and sixth contacts when said movable contact means is in said first position to thereby interconnect said first and second sections in parallel circuit relation with each other and in series circuit relation with said third section between said first and second circuit points to provide a predetermined transformation ratio vbetween said primary and secondary windings; said first contact member being in engagement with and interconnecting said first and third contacts, and said third contact member being in engagement with and interconnecting said fifth and sixth contacts when said movable contact mean-s is in said second position to thereby interconnect said first, second and third sections and said second pair of fuses in series circuit relation with each other between said first and second circuit points to provide a second predetermined transformation ratio between said primary and secondary windings.

6. A transformer comprising a primary winding for connection to a source of supply voltage, a secondary winding for connection toa load, a pair of terminals, one of said windings having a predetermined number of winding turns, first and second pr-otective circuit interrupting means, and .means for connecting said one winding selec'- tively in first and second winding arrangements between said terminals to respectively effect first and second transformation ratios between said primary and secondary windings, said one winding when in said first winding arrangement having a preselected number of said winding turns connected in series with each other and said first circuit interrupting means and in series with a winding circuit including a plurality of parallel-connected winding sections each having an equal number of said winding turns, all of said preselected number of winding turns and the winding turns of said winding sections together definingall of the winding turns of said one winding, all of said winding turns of said one winding being connected in series with each other and said second circuit interrupting means when said one winding is in said second winding arrangement.

l7. The transformer according to claim 6, wherein said preselected number of turns is different from the number of turns in each of said winding sections.

8. The transformer according to claim 7, wherein said first circuit interrupting means is connected between one of said terminals and said one winding t-o carry the total curr-ent of said one winding in both of said first and second winding arrangements.

9. The transformer according to claim 8, wherein said connecting means` includes means for effectively disconnecting said second circuit interrupting means from said one winding when said one winding is in said first winding arrangement.

y10. The transformer according to claim 7, wherein said first and second circuit interrupting means comprise first and second fuses, respectively, and said transformer further includes third and fourth fuses, said first fuse being connected between one of said termin-als and one end of said one Winding and said third fuse being connected between the other of said terminals and the opposite e end of said one winding when said one winding is in said first winding arrangement, said second fuse being connected between said one terminal and said one end of said winding and said fourth fuse being connected between said other terminal and said opposite end of said `one winding -when said one winding is in said secon-d winding arrangement, said first and third yfuses being of a higher current rating than that of said second and fourth fuses and also being connected to carry the total current of said one winding when said one winding is in said second winding arrangement.

11. A transformer 4comprising primary and secondary windings, a pair of terminals adapted for connection to a source of alternating current, .first and second protective circuit interrupting-means, and switch means connected with said primary winding and said first and second protective circuit interrupting means and having first and second operating positions for selectively connecting said primary winding respectively in first and second winding arrangement between said terminals, said primary winding when in said first winding arrangement having a first portion thereof connected in series with said first circuit interrupting means and in series with a winding circuit including a plurality of other portions of said primary winding connected in parallel with each other to provide a first predetermined transformation ratio between said primary and secondary windings, said first portion having a different number of primary winding turns than each of said other portions, each of said other portions having an equal number of primary winding turns, all of the winding turns in said other portions and in said first portion together defining all of the winding turns of said primary winding, all -of said winding turns of said primary winding being connected in series with each other and said second circuit interrupting means when said primary winding is in said second winding arrangement to provide a second translformation ratio between said primary and secondary windings.

12. The transformer according to claim 11, wherein said first circuit interrupting means is connected between one of said terminals and said primary winding to carry the total current of said primary winding in both of said first and sec-ond winding arrangements.

13. The transformer according to claim 12, wherein said switch means includes means for effectively disconnecting said se-cond circuit interrupting means from said primary winding when said primary Winding is in said first winding arrangement.

14. The transformer according to claim 12, wherein said first and second circuit interrupting means comprise first and second fuses, respectively, and said first fuse has a higher current rating than said second fuse.

1S. The transformer laccording to claim 14, including a casing enclosing said primary and secondary windings and said switch means, and at least one primary .bushing connected to said casing, said first fuse being connected to said bushing, said one terminal being connected to said bushing and said kfirst fuse.

16. The transformer according to claim 11, including third and fourth protective circuit interrupting means, said first circuit interrupting means being connected bctween one of said terminals and one end of said primary 4winding and said third circuit interrupting means being connected between the other of said terminals and the opposite end of said primary winding when said switch is in said first operating position, sai-d second circuit interrupting means being connected between said one terminal and said one end of said primary Winding and said fourth circuit interrupting means being connected between said other terminal and said opposite end of said primary winding when said switch is in said second operating position.

17. The transformer according to claim 16, wherein said first, second, third and fourth circuit interrupting means are respectively first, second, third and fourth fuses and wherein said first and third fuses have a higher current rating than said second and fourth fuses and wherein all of said fuses are connected in series `with said primary winding when said primary winding is in said second winding arrangement.

18'. The transformer according to claim 17, including a casing enclosing said primary and secondary windings and said switch Imeans, a pair of primary bushings connected to said casing, and means connecting said first and third Ifuses to said terminals respectively through said bushings.

19. The transformer according to claim 17, wherein said second fuse is effectively disconnected from said primary winding and said fourth fuse is connected in said winding circuit in series with one of said other portions and in parallel with the other of said other porti-ons when said primary winding is in said first winding arrangement.

References Cited UNITED STATES PATENTS 4/1963 Porter 317--14 8/1965 Nygren 323-49 

